CN113474919B

CN113474919B - Positive electrode active material for secondary battery and secondary battery

Info

Publication number: CN113474919B
Application number: CN202080012652.0A
Authority: CN
Inventors: 黄木淳史; 远藤晋; 早崎真治; 高桥翔; 藤川隆成; 仓冢真树
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 2019-02-06
Filing date: 2020-01-29
Publication date: 2023-09-22
Anticipated expiration: 2040-01-29
Also published as: JPWO2020162277A1; CN113474919A; US20210367230A1; JP7078141B2; WO2020162277A1

Abstract

The positive electrode active material for a secondary battery is provided with: a center portion including a layered rock salt type lithium nickel composite oxide; and a covering portion that covers a surface of the center portion and includes a boron compound. The crystallite size of the (104) crystal face calculated by using an X-ray diffraction method and a Scherrer's formula is 40.0nm or more and 74.5nm or less. The specific surface area measured by BET specific surface area measurement method satisfies the conditions of-0.0160 XZ+1.72.ltoreq.A.ltoreq.0.0324 XZ+2.94 (Z is crystallite size (nm), A is specific surface area (m) ² /g)). The first element concentration ratio calculated from a C1s spectrum, an O1s spectrum, and the like measured by an X-ray photoelectron spectroscopy method is 0.08 to 0.80, the second element concentration ratio is 0.60 to 1.50, and the third element concentration ratio is 0.15 to 0.90.

Description

Positive electrode active material for secondary battery and secondary battery

Technical Field

The present technology relates to a positive electrode active material for a secondary battery comprising a layered rock salt type lithium nickel composite oxide, and a secondary battery using the same.

Background

Various electronic devices such as mobile phones are widely used. Accordingly, a secondary battery, which is small and lightweight and can obtain high energy density, has been developed as a power source. The secondary battery includes a positive electrode including a positive electrode active material, a negative electrode, and an electrolyte.

The structure of the positive electrode active material affects the battery characteristics of the secondary battery, and thus various studies have been made on the structure of the positive electrode active material. Specifically, in order to improve the thermal stability, a particulate lithium composite oxide (Li _x Ni _y Co _z X _(1-y-z) Ow) (for example, refer to patent document 1). In order to improve cycle characteristics and the like, a particulate lithium composite oxide (Li _x Ni _1-y M _y O ₂₊ α) (for example, refer to patent document 2). In order to improve the output characteristics, a lithium composite oxide (Li) in which a peak intensity ratio calculated from the analysis result of the X-ray photoelectron spectroscopy is set so as to fall within a predetermined range is used _x (Ni _1-y Co _y ) _1- _z M _z O ₂ ) (for example, refer to patent document 3).

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 2004-335278

Patent document 2: international publication 2012/133436 pamphlet

Patent document 3: japanese patent laid-open No. 2004-327246

Disclosure of Invention

Electronic devices mounted with secondary batteries are increasingly becoming higher in performance and multifunctional. Therefore, the frequency of use of electronic devices is increasing, and the environment of use of electronic devices is expanding. As a result, there is still room for improvement in battery characteristics of the secondary battery.

The present technology has been made in view of the above-described problems, and an object thereof is to provide a positive electrode active material for a secondary battery and a secondary battery that can obtain excellent battery characteristics.

The positive electrode active material for a secondary battery according to one embodiment of the present technology comprises: a central portion containing a layered rock salt type lithium nickel composite oxide represented by the following formula (1); and a covering portion that covers a surface of the center portion and includes a boron compound. The crystallite size of the (104) crystal face calculated by using an X-ray diffraction method and a Scherrer's formula is 40.0nm or more and 74.5nm or less. The specific surface area measured by the BET specific surface area measurement method satisfies the condition represented by the following formula (2). The first element concentration ratio calculated from a C1s spectrum and an O1s spectrum measured by an X-ray photoelectron spectroscopy and represented by the following formula (3) is 0.08 or more and 0.80 or less. Based on Li1s spectrum and Ni2p spectrum measured by X-ray photoelectron spectroscopy _3/2 Spectrogram, co2p _3/2 Spectrogram, mn2p _1/2 The second element concentration ratio calculated from the spectrum and the Al2s spectrum and represented by the following formula (4) is 0.60 or more and 1.50 or less. From B1s spectra, ni2p, measured by X-ray photoelectron spectroscopy _3/2 Spectrogram, co2p _3/2 Spectrogram, mn2p _1/2 The third element concentration ratio calculated from the spectrum and the Al2s spectrum and represented by the following formula (5) is 0.15 or more and 0.90 or less.

Li _a Ni _1-b M _b O _c ···(1)

( M is at least one of cobalt (Co), iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), aluminum (Al), chromium (Cr), vanadium (V), titanium (Ti), magnesium (Mg) and zirconium (Zr). a. b and c satisfy 0.8 < a < 1.2, 0.ltoreq.b.ltoreq.0.4 and 0 < c < 3 )

-0.0160×Z+1.72≤A≤-0.0324×Z+2.94···(2)

The crystallite size (nm) of the (Z-104) crystal face A is the specific surface area (m ² /g))

R1＝I1/I2···(3)

(R1 is the concentration ratio of the first element. I1 is calculated from the C1s spectrumCalculated CO ₃ Concentration (atomic%). I2 is the Me-O concentration (atomic%) calculated from the O1s spectrum. Wherein Me-O is an oxide derived from O bonded to Li, ni or M in the formula (1) and having a spectrum detected in a range of bond energy of 528eV to 531eV

R2＝I3/I4···(4)

(R2 is the second element concentration ratio. I3 is the Li concentration (atomic%) calculated from the Li1s spectrum. I4 is Ni2p _3/2 Spectrogram, co2p _3/2 Spectrogram, mn2p _1/2 The sum of Ni concentration (atomic%), co concentration (atomic%), mn concentration (atomic%) and Al concentration (atomic%) calculated from the spectrogram and Al2s spectrogram

R3＝I5/I4···(5)

(R3 is the concentration ratio of the third element. I4 is according to Ni2p _3/2 Spectrogram, co2p _3/2 Spectrogram, mn2p _1/2 The sum of the Ni concentration (at%), co concentration (at%), mn concentration (at%) and Al concentration (at%) calculated from the spectra and Al2s spectra. I5 is the B concentration (atomic%) calculated from the B1s spectrum

The secondary battery according to one embodiment of the present technology includes a positive electrode including a positive electrode active material having the same structure as the positive electrode active material for the secondary battery according to the above-described embodiment of the present invention, a negative electrode, and an electrolyte.

According to the positive electrode active material for a secondary battery or the secondary battery according to an embodiment of the present technology, since the positive electrode active material has the above-described structure and physical properties, excellent battery characteristics can be obtained.

The effects of the present technology are not necessarily limited to those described herein, and may be any of a series of effects related to the present technology described below.

Drawings

Fig. 1 is an exploded perspective view showing the structure of a secondary battery according to an embodiment of the present technology.

Fig. 2 is a cross-sectional view showing the structure of the electrode body shown in fig. 1.

Fig. 3 is a plan view showing the structure of the positive electrode current collector shown in fig. 2.

Fig. 4 is a plan view showing the structure of the negative electrode current collector shown in fig. 2.

Fig. 5 is a plan view schematically showing the structure of a positive electrode active material according to an embodiment of the present technology.

Fig. 6 is a diagram showing an appropriate range regarding the specific surface area (crystallite size) of the positive electrode active material.

Fig. 7 is a plan view for explaining an analysis range of an X-ray photoelectron spectroscopy and a measurement range of a warder method (titration method).

Fig. 8 is a diagram showing an example of a volume-based particle size distribution of the positive electrode active material.

Fig. 9 is an exploded perspective view showing the structure of a secondary battery according to modification 1.

Detailed Description

An embodiment of the present technology will be described in detail below with reference to the drawings. Further, the order of description is as follows.

1. Secondary battery

1-1 Structure

1-1-1. Integral Structure

1-1-2 Structure and Properties of Positive electrode active Material

1-2. Action

1-3 method of manufacture

1-3-1. Method for producing positive electrode active material

1-3-2 method for manufacturing secondary battery

1-4. Actions and effects

2. Modification examples

3. Use of secondary battery

<1 > Secondary Battery >

First, a secondary battery according to an embodiment of the present technology will be described. In addition, since the positive electrode active material for a secondary battery according to an embodiment of the present technology (hereinafter, simply referred to as "positive electrode active material") is a part (a component) of the secondary battery described herein, the positive electrode active material will be described together.

As described later, this secondary battery is a lithium ion secondary battery that uses the intercalation and deintercalation of lithium (lithium ions) to obtain a battery capacity.

<1-1. Structure >

Hereinafter, the overall structure of the secondary battery will be described, and the structure and physical properties of the positive electrode active material will be described.

<1-1-1. Structure of the whole >

Fig. 1 shows an exploded perspective structure of a secondary battery 10 as a secondary battery according to an embodiment of the present technology. Fig. 2 shows a cross-sectional structure of the electrode body 20 shown in fig. 1. Fig. 3 shows a top view of the positive electrode current collector 21A shown in fig. 2, and fig. 4 shows a top view of the negative electrode current collector 22A shown in fig. 2.

In fig. 1, the electrode body 20 and the outer package member 30 (the first member 30A and the second member 30B) are shown separated from each other. Fig. 2 shows a state before the plurality of positive electrode collectors 21A (positive electrode collector exposed portions 21N shown in fig. 3) are joined to each other, and shows a state before the plurality of negative electrode collectors 22A (negative electrode collector exposed portions 22N shown in fig. 4) are joined to each other.

As shown in fig. 1, for example, the secondary battery 10 includes a stacked electrode assembly 20 as a battery element and a film-shaped outer packaging member 30. That is, the secondary battery 10 described herein is, for example, a laminated film type nonaqueous electrolyte secondary battery in which the rectangular electrode body 20 is accommodated in the exterior package member 30. The secondary battery 10 can be miniaturized, light-weighted, and thinned.

A positive electrode lead 11 and a negative electrode lead 12 are mounted on the electrode body 20. The electrode body 20 has a main surface 20A and a main surface 20B located on the opposite side of the main surface 20A, the main surface 20A having a longitudinal side portion 20C and a width side portion 20D.

The positive electrode lead 11 and the negative electrode lead 12 are led out from the inside of the outer package member 30 to the outside in the same direction, and are, for example, thin plate-like or mesh-like. The positive electrode lead 11 and the negative electrode lead 12 include, for example, a metal material such as aluminum, copper, nickel, or stainless steel.

An adhesive film 13 for preventing the invasion of outside air is interposed between the outer package member 30 and the positive electrode lead 11, and the adhesive film 13 is interposed between the outer package member 30 and the negative electrode lead 12 in the same way. The adhesive film 13 includes a material having adhesion to the positive electrode lead 11 and the negative electrode lead 12, and is, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

[ external packaging Member ]

The outer package member 30 has flexibility (flexibility), for example, and accommodates the electrode body 20 (the positive electrode 21, the negative electrode 22, the electrolyte, and the like). The outer package member 30 includes, for example, two films (a first member 30A and a second member 30B) separated from each other, and the first member 30A and the second member 30B are stacked on each other with the electrode body 20 interposed therebetween. Since the four sides of each of the first member 30A and the second member 30B are in close contact with each other, the peripheral edge portions of each of the first member 30A and the second member 30B form a close contact portion. The first member 30A has a housing portion 31 for housing the electrode body 20, and the housing portion 31 is formed by, for example, deep drawing.

The outer package member 30 is, for example, a laminate film in which a heat-fusible resin layer, a metal layer, and a surface protective layer are laminated in this order from the inside (the side closer to the electrode body 20). The heat-fusible resin layer contains a polymer material such as polypropylene or polyethylene, for example. The metal layer includes, for example, a metal material such as aluminum. The surface protective layer includes a polymer material such as nylon. Specifically, the outer package member 30 is, for example, an aluminum laminate film formed by laminating a polyethylene film, an aluminum foil, and a nylon film in this order from the inside. The outer edge portions (heat-fusible resin layers) of the first member 30A and the second member 30B are mutually adhered to each other by, for example, a fusion process or an adhesive.

However, instead of the aluminum laminate film, the outer package member 30 may be a laminate film having another laminated structure, a polymer film such as polypropylene, or a metal film. The outer package 30 may be a laminated film in which a polymer film is laminated on one or both surfaces of an aluminum foil.

[ electrode body ]

As shown in fig. 1 and 2, for example, the electrode body 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte solution as a liquid electrolyte. In the electrode body 20, a plurality of positive electrodes 21 and a plurality of negative electrodes 22 are alternately laminated with separators 23 interposed therebetween, and the positive electrodes 21, the negative electrodes 22, and the separators 23 are impregnated with an electrolyte solution, respectively.

In this secondary battery 10, in order to prevent precipitation of lithium metal from the surface of the negative electrode 22 during charging, the electrochemical capacity per unit area of the negative electrode 22 is preferably larger than the electrochemical capacity per unit area of the positive electrode 21.

[ Positive electrode ]

As shown in fig. 2, for example, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B provided on both sides of the positive electrode current collector 21A. However, the positive electrode active material layer 21B may be provided only on one side of the positive electrode current collector 21A.

As shown in fig. 3, the positive electrode collector 21A includes, for example, a rectangular positive electrode active material layer forming portion 21M that forms the positive electrode active material layer 21B, and a rectangular positive electrode collector exposure portion 21N that does not form the positive electrode active material layer 21B. The positive electrode active material layer 21B is formed on both sides of the positive electrode active material layer forming portion 21M, for example, as described above. The positive electrode current collector exposed portion 21N is a portion of the positive electrode active material layer forming portion 21M extending and having a width smaller than the width (the dimension in the X axis direction) of the positive electrode active material layer forming portion 21M. However, as shown by the two-dot chain line in fig. 3, the positive electrode current collector exposed portion 21N may have the same width as the positive electrode active material layer formed portion 21M. The plurality of positive electrode current collector exposed portions 21N are bonded to each other, and the positive electrode lead 11 is bonded to the plurality of positive electrode current collector exposed portions 21N bonded to each other.

The positive electrode current collector 21A is a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode active material layer 21B contains a positive electrode active material capable of intercalating and deintercalating lithium as an electrode reaction material, and the positive electrode active material is in the form of a plurality of particles. The positive electrode active material layer 21B may contain any one or two or more of additives such as a binder and a conductive agent as necessary.

The positive electrode active material contains any one or two or more of positive electrode materials capable of intercalating and deintercalating lithium, and the positive electrode material contains a lithium-containing compound. The lithium-containing compound is a generic term for a compound containing lithium (Li) as a constituent element.

Specifically, the lithium-containing compound is a layered rock salt type lithium nickel composite oxide represented by the following formula (1). That is, the lithium nickel composite oxide has a layered rock salt type crystal structure. This is because a high battery capacity can be stably obtained even if the battery voltage is low. Further, since the composition (a) of lithium varies depending on the charge-discharge state, the value of a represents the value of the complete discharge state.

Li _a Ni _1-b M _b O _c ···(1)

As is clear from the formula (1), the lithium nickel composite oxide is a composite oxide containing nickel (Ni) as a constituent element together with lithium, and may contain any one or two or more additional metal elements (M) as required.

Specifically, the lithium nickel composite oxide contains, for example, any one or two or more compounds represented by the following formulas (1-1), (1-2) and (1-3), respectively.

Li _a Ni _1-b-c-d Co _b Al _c M1 _d O _e ···(1-1)

( M1 is at least one of iron (Fe), copper (Cu), zinc (Zn), chromium (Cr), vanadium (V), titanium (Ti), magnesium (Mg) and zirconium (Zr). a. b, c, d and e satisfy 0.8 < a < 1.2, 0.ltoreq.b.ltoreq.0.2, 0.ltoreq.c.ltoreq.0.1, 0.ltoreq.d.ltoreq.0.1, 0 < e < 3 and 0.ltoreq.b+c+d.ltoreq.0.3 )

Li _a Ni _1-b-c-d Co _b Mn _c M2 _d O _e ···(1-2)

( M2 is at least one of iron (Fe), copper (Cu), zinc (Zn), chromium (Cr), vanadium (V), titanium (Ti), magnesium (Mg) and zirconium (Zr). a. b, c, d and e satisfy 0.8 < a < 1.2, 0.ltoreq.b.ltoreq.0.4, 0.ltoreq.c.ltoreq.0.4, 0.ltoreq.d.ltoreq.0.1, 0 < e < 3 and 0.1.ltoreq.b+c+d.ltoreq.0.7 )

Li _a Ni _1-b-c-d-e Co _b Mn _c Al _d M3 _e O _f ···(1-3)

( M3 is at least one of iron (Fe), copper (Cu), zinc (Zn), chromium (Cr), vanadium (V), titanium (Ti), magnesium (Mg) and zirconium (Zr). a. b, c, d, e and f satisfy 0.8 < a < 1.2, 0 < b < 0.2, 0 < c < 0.1, 0 < d < 0.1, 0 < e < 0.1, 0 < f < 3 and 0 < (b+c+d+e) < 0.3 )

The compound represented by the formula (1-1) is a nickel-cobalt-aluminum lithium-nickel composite oxide. The compound represented by the formula (1-2) is a nickel-cobalt-manganese lithium-nickel composite oxide. The compound represented by the formula (1-3) is a nickel-cobalt-manganese-aluminum lithium-nickel composite oxide. However, when the compound represented by both the formula (1-1) and the formula (1-2) is present, the compound corresponds to the compound represented by the formula (1-1).

More specifically, the compound represented by the formula (1-1) is, for example, liNiO ₂ 、LiNi _0.9 Co _0.1 O ₂ 、LiNi _0.85 Co _0.1 Al _0.05 O ₂ 、LiNi _0.90 Co _0.05 Al _0.05 O ₂ 、LiNi _0.82 Co _0.14 Al _0.04 O ₂ 、LiNi _0.78 Co _0.18 Al _0.04 O ₂ And LiNi _0.90 Co _0.06 Al _0.04 O ₂ Etc. The compound represented by the formula (1-2) is, for example, liNi _0.5 Co _0.2 Mn _0.3 O ₂ 、LiNi _0.8 Co _0.1 Mn _0.1 O ₂ 、LiNi _0.9 Co _0.05 Mn _0.05 O ₂ 、LiNi _0.3 Co _0.3 Mn _0.3 O ₂ And LiNi _0.84 Co _0.08 Mn _0.08 O ₂ Etc. The compound represented by the formula (1-3) is, for example, liNi _0.80 Co _0.10 Mn _0.05 Al _0.05 O ₂ Etc.

In particular, the surface of the lithium nickel composite oxide is covered with a boron compound. That is, the positive electrode active material (positive electrode material) contains a boron compound covering the surface of the lithium nickel composite oxide together with the lithium nickel composite oxide. The boron compound contains boron (B) as a componentThe compounds of the constituent elements are collectively referred to. This is because the surface of the lithium nickel composite oxide is electrochemically stabilized, and thus the decomposition reaction of the electrolyte solution on the surface of the lithium nickel composite oxide is suppressed. The kind of the boron compound is not particularly limited, and is, for example, boric acid (H ₃ BO ₃ ) Lithium tetraborate (Li) ₂ B ₄ O ₇ ) Ammonium pentaborate (NH) ₄ B ₅ O ₈ ) Lithium metaborate (LiBO) ₂ ) And boron oxide (B) ₂ O ₃ ) Etc.

The positive electrode active material including the lithium nickel composite oxide covered with the boron compound as the positive electrode material has a predetermined structure and physical properties in order to improve the battery characteristics of the secondary battery 10. Details of the structure and physical properties of the positive electrode active material will be described later.

The positive electrode active material may contain any one or two or more of other positive electrode materials (other lithium-containing compounds). The other lithium-containing compound may be a layered rock salt type other lithium-containing compound, a spinel type lithium-containing compound, or an olivine type lithium-containing compound. Other lithium-containing compounds of the lamellar rock salt type, e.g. LiCoO ₂ And lithium composite oxide. Spinel-type lithium-containing compounds, e.g. LiMn ₂ O ₄ And lithium composite oxide. Olivine-type lithium-containing compounds, e.g. LiFePO ₄ 、LiMnPO ₄ And LiMn _0.5 Fe _0.5 PO ₄ And lithium phosphate compounds.

The positive electrode active material may contain any one or two or more of compounds (lithium-free compounds) containing no lithium as a constituent element. The lithium-free compounds being, for example, mnO ₂ 、V ₂ O ₅ 、V ₆ O ₁₃ Inorganic compounds such as NiS and MoS.

The binder may be one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, styrene-butadiene rubber, and carboxymethyl cellulose. However, the binder may be, for example, a copolymer of two or more polymer materials.

The conductive agent contains, for example, any one or two or more of carbon materials such as graphite, carbon black, ketjen black, and the like. However, the conductive agent may be a metal material or a conductive polymer material as long as it is a material having conductivity, for example.

[ negative electrode ]

As shown in fig. 2, for example, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B provided on both sides of the negative electrode current collector 22A. However, the anode active material layer 22B may be provided only on one side of the anode current collector 22A.

As shown in fig. 4, the negative electrode current collector 22A includes, for example, a rectangular negative electrode active material layer forming portion 22M that forms the negative electrode active material layer 22B, and a rectangular negative electrode current collector exposing portion 22N that does not form the negative electrode active material layer 22B. The anode active material layer 22B is formed on both sides of the anode active material layer forming portion 22M, for example, as described above. The anode current collector exposed portion 22N is a portion of the anode active material layer forming portion 22M extending and provided with a width smaller than the width (the dimension in the X axis direction) of the anode active material layer forming portion 22M. The negative electrode current collector exposed portion 22N is disposed so as not to overlap with the positive electrode current collector exposed portion 21N. However, as shown by the two-dot chain line in fig. 4, the anode current collector exposure portion 22N may have the same width as the anode active material layer formation portion 22M. The plurality of negative electrode current collector exposed portions 22N are bonded to each other, and the negative electrode lead 12 is bonded to the plurality of negative electrode current collector exposed portions 22N bonded to each other.

The negative electrode current collector 22A is a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. The anode active material layer 22B contains, for example, an anode active material capable of intercalating and deintercalating lithium as an electrode reaction material. The negative electrode active material layer 22B may contain any one or two or more of additives such as a binder and a conductive agent, if necessary. Details of the binder and the conductive agent are as described above.

The negative electrode active material includes any one or two or more of negative electrode materials capable of intercalating and deintercalating lithium, and examples of the negative electrode materials include carbon materials and metal materials. Of course, the negative electrode material may be both (mixture of) a carbon material and a metal-based material.

Examples of the carbon material include non-graphitizable carbon, graphite, pyrolytic carbon, coke, vitreous carbon, calcined organic polymer compound, carbon fiber, activated carbon, and the like.

The metal-based material is a material containing any one or two or more of a metal element and a metalloid element as constituent elements. The metal material may be an alloy, a compound, or a mixture. The metal material may be crystalline or amorphous. The metal element and the metalloid element are, for example, magnesium (Mg), boron (B), aluminum (Al), titanium (Ti), gallium (Ga), indium (In), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y), palladium (Pd), platinum (Pt), and the like. The alloy may be an alloy composed of two or more metal elements, may contain one or more metal elements and one or more metalloid elements, and may contain one or more nonmetallic elements. The structure of the alloy is, for example, a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or a coexisting structure of two or more of these. The compound is, for example, an oxide or the like.

The negative electrode material may be, for example, a metal oxide, a polymer material, or the like. The metal oxide is, for example, a lithium composite oxide such as lithium titanate (Li) ₄ Ti ₅ O ₁₂ ) And lithium titanium composite oxide. The polymer material is, for example, polyacetylene, polyaniline, polypyrrole, or the like.

[ diaphragm ]

The separator 23 is interposed between the positive electrode 21 and the negative electrode 22, and allows lithium ions to pass therethrough while preventing a short circuit due to contact between the positive electrode 21 and the negative electrode 22. The separator 23 may be a porous film containing one or more of a polymer material and a ceramic material, or may be a laminate of two or more porous films. The polymer material may be, for example, polyethylene, polypropylene, polytetrafluoroethylene, or the like, and may be a mixture of two or more of these, or may be a copolymer of two or more of these.

[ electrolyte ]

The electrolyte solution contains a solvent and an electrolyte salt, and may contain any one or two or more additives.

The solvent is, for example, a nonaqueous solvent, and the electrolyte containing the nonaqueous solvent is a so-called nonaqueous electrolyte. The type of the solvent (nonaqueous solvent) may be one type or two or more types.

Specifically, the nonaqueous solvent is, for example, a cyclic carbonate, a chain carbonate, a lactone, a chain carboxylate, a nitrile (mononitrile) compound, an unsaturated cyclic carbonate, a halogenated carbonate, a sulfonate, an acid anhydride, a dicyano compound (dinitrile compound), a diisocyanate compound, a phosphate, or the like. This is because excellent capacity characteristics, cycle characteristics, storage characteristics, and the like can be obtained.

Examples of the cyclic carbonates include ethylene carbonate, propylene carbonate and butylene carbonate. Examples of the chain carbonates include dimethyl carbonate, diethyl carbonate and methylethyl carbonate. The lactones are, for example, gamma-butyrolactone and gamma-valerolactone. Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The nitrile compound is, for example, acetonitrile, methoxyacetonitrile, 3-methoxypropionitrile, succinonitrile, adiponitrile, etc. The unsaturated cyclic carbonates are, for example, vinylene carbonate, vinyl ethylene carbonate, methylene ethylene carbonate, and the like. The halogenated carbonates are, for example, 4-fluoro-1, 3-dioxolan-2-one, 4, 5-difluoro-1, 3-dioxolan-2-one, fluoromethyl carbonate and the like. The sulfonic acid ester is, for example, 1, 3-propane sultone, 1, 3-propenoic acid lactone, or the like. The acid anhydride is, for example, succinic anhydride, glutaric anhydride, maleic anhydride, ethane disulfonic anhydride, propane disulfonic anhydride, sulfobenzoic anhydride, sulfopropionic anhydride, sulfobutyric anhydride, or the like. The dinitrile compounds are, for example, succinonitrile, glutaronitrile, adiponitrile, phthalonitrile and the like. The diisocyanate compound is, for example, hexamethylene diisocyanate or the like. The phosphoric acid ester is, for example, trimethyl phosphate, triethyl phosphate, or the like.

In addition, the nonaqueous solvent may be, for example, N-dimethylformamide, N-methylpyrrolidone, N-methyloxazolidinone, nitromethane, nitroethane, sulfolane, dimethylsulfoxide, and ethylenesulfide.

The electrolyte salt is, for example, a light metal salt such as a lithium salt. The type of the electrolyte salt (lithium salt) may be one type or two or more types. The content of the electrolyte salt is not particularly limited, and is, for example, 0.3mol/kg to 3.0mol/kg with respect to the solvent.

Specifically, the lithium salt is, for example, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium trifluoromethanesulfonate, lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethanesulfonyl) imide, lithium bis (pentafluoroethanesulfonyl) imide, lithium tris (trifluoromethanesulfonyl) methyllithium, lithium chloride, lithium bromide, lithium fluorophosphate, lithium difluorophosphate, lithium bis (oxalato) borate, or the like.

<1-1-2. Structure and physical Properties of Positive electrode active Material >

Fig. 5 schematically shows a top view of a positive electrode active material 100 as a positive electrode active material according to an embodiment of the present technology.

As shown in fig. 5, the positive electrode active material 100 includes a central portion 110 and a cover portion 120 that covers the surface of the central portion 110. The center portion 110 is in the form of a plurality of particles and includes the above-described lithium nickel composite oxide. The covering portion 120 contains the boron compound described above. As shown in fig. 5, the cover 120 may cover the entire surface of the center 110, or may cover only a part of the surface of the center 110.

In the positive electrode active material 100, for example, a plurality of primary particles G1 including a lithium nickel composite oxide are collected, and therefore, secondary particles G2 (the central portion 110) are formed from the plurality of primary particles G1. Thereby, the boron compound (covering portion 120) covers the surface of the secondary particle G2, for example. Further, it is considered that a part of the boron compound is solid-dissolved in the primary particles G1.

The positive electrode active material 100 has a predetermined structure and physical properties to improve the battery characteristics of the secondary battery 10, as described above, in which the central portion 110 (lithium nickel composite oxide) of the surface is covered with the covering portion 120 (boron compound). The following describes the necessary conditions of the positive electrode active material 100, and then describes arbitrary conditions of the positive electrode active material 100.

[ essential conditions ]

Specifically, the following five conditions (first to fifth conditions) are satisfied in relation to the structure and physical properties of the positive electrode active material 100.

(first condition)

The crystallite size Z (nm) of the (104) crystal face of the positive electrode active material 100 calculated using an X-ray diffraction (XRD) method and Scherrer's formula is 40.0nm to 74.5nm.

(second condition)

Specific surface area a (m) of positive electrode active material 100 measured by BET specific surface area measurement method ² And/g) satisfies the condition shown in the following formula (2). Wherein the value of "-0.0160 xz" for calculating the lower limit value is a value obtained by rounding the third bit of the decimal point, and the value of "-0.0324 xz" for calculating the upper limit value is a value obtained by rounding the third bit of the decimal point. Hereinafter, the range of the specific surface area a shown in the formula (2), that is, the range of the specific surface area a defined in the relation with the crystallite size Z is referred to as "proper range". The theory of derivation of the appropriate range of the specific surface area a described here will be described later.

-0.0160×Z+1.72≤A≤-0.0324×Z+2.94···(2)

(Z is the crystallite size (nm) of the (104) crystal face of the positive electrode active material 100. A is the specific surface area (m) of the positive electrode active material 100 ² /g))

Fig. 6 shows an appropriate range regarding the specific surface area a (crystallite size Z) of the positive electrode active material 100. In FIG. 6, the horizontal axis represents crystallite size Z (nm), and the vertical axis represents specific surface area A (m ² /g)。

According to the first condition and the second condition described above, as shown in fig. 6, the ranges of values that can be taken by the crystallite size Z and the specific surface area a are the range Q defined by two straight lines L (solid line L1 and broken line L2), respectively. In fig. 6, shading is applied in the range Q. When the specific surface area a=y and the crystallite size z=x, the solid line L1 is a straight line indicated by y= -0.0324x+2.94, and the broken line L2 is a straight line indicated by y= -0.0160x+1.72.

(third condition)

The element concentration ratio calculated from the carbon (C) 1s spectrum and the oxygen (O) 1s spectrum of the positive electrode active material 100 measured by the X-ray photoelectron spectroscopy (X-ray Photoelectron Spectroscopy (XPS)), that is, the element concentration ratio R1 (first element concentration ratio) represented by the following formula (3), is 0.08 to 0.80. The element concentration ratio R1 is considered to be a residual lithium component (Li ₂ CO ₃ ) Is a parameter of the distribution state of the (c).

R1＝I1/I2···(3)

(R1 is the element concentration ratio. I1 is CO calculated from the C1s spectrum ₃ Concentration (atomic%). I2 is the Me-O concentration (atomic%) calculated from the O1s spectrum. Wherein Me-O is an oxide derived from O bonded to Li, ni or M in the formula (1) and having a spectrum detected in a range of bond energy of 528eV to 531eV

(fourth condition)

Based on lithium (Li) 1s spectrum and nickel (Ni) 2p of positive electrode active material 100 measured by XPS _3/2 Spectrogram, cobalt (Co) 2p _3/2 Spectrogram, manganese (Mn) 2p _1/2 The other element concentration ratio calculated from the spectrum and the aluminum (Al) 2s spectrum, that is, the element concentration ratio R2 (second element concentration ratio) represented by the following formula (4) is 0.60 to 1.50. The element concentration ratio R2 is considered to be a parameter mainly indicating the distribution state of lithium on the surface of the positive electrode active material 100.

R2＝I3/I4···(4)

(R2 is the element concentration ratio. I3 is the Li concentration (atomic%) calculated from the Li1s spectrum. I4 is Ni2p _3/2 Spectrogram, co2p _3/2 Spectrogram, mn2p _1/2 The sum of Ni concentration (atomic%), co concentration (atomic%), mn concentration (atomic%) and Al concentration (atomic%) calculated from the spectrogram and Al2s spectrogram

(fifth condition)

Based on boron (B) 1s spectrum, ni2p of positive electrode active material 100 measured by XPS _3/2 Spectrogram, co2p _3/2 Spectrogram, mn2p _1/2 The spectrogram and the Al2s spectrogram are calculated to obtain still another element concentration ratio, namely, an element concentration ratio R3 (third element concentration ratio) shown in the following formula (5) is 0.15-0.90. Consider the elementThe element concentration ratio R3 is a parameter indicating the distribution state of boron on the surface of the positive electrode active material 100.

R3＝I5/I4···(5)

Regarding the positive electrode active material 100 including the central portion 110 (lithium nickel composite oxide) and the covering portion 120 (boron compound), the first condition and the second condition are satisfied because the specific surface area a is optimized in relation to the crystallite size Z. Thus, the decomposition reaction of the electrolyte is suppressed on the surface of the reactive positive electrode active material 100, and the generation of unnecessary gas due to the decomposition reaction of the electrolyte is also suppressed. Accordingly, even if charge and discharge are repeated, it is considered that the discharge capacity is not easily lowered and gas is not easily generated.

In addition, in the case where the first condition and the second condition are satisfied, the third condition, the fourth condition, and the fifth condition are further satisfied because the surface state (the distribution state of each of lithium, boron, and residual lithium components) of the positive electrode active material 100 is optimized. That is, the surface of the center portion 110 is appropriately covered with the covering portion 120 while appropriately suppressing the residual amount of the residual lithium component on the surface of the positive electrode active material 100. Accordingly, while suppressing the generation of gas due to the residual lithium component, the input and output of lithium ions to and from the center portion 110 are facilitated, and the decomposition reaction of the electrolyte solution on the surface of the center portion 110 is suppressed. In this case, in particular, even when the secondary battery 10 (positive electrode active material 100) is used (charged and discharged) or stored in a high-temperature environment, it is considered that the decomposition reaction of the electrolyte can be effectively suppressed.

The residual lithium component is an unnecessary component that remains in the positive electrode active material 100 during the production process of the positive electrode active material 100. The residual lithium component is, for example, lithium carbonate (Li) ₂ CO ₃ ) And lithium hydroxide (LiOH), which is formedIs a main cause of gas generation unnecessary at the time of charge and discharge of the secondary battery 10.

(measurement method and measurement conditions)

The details of the measurement method and measurement conditions of a series of parameters related to the above-described five conditions (first to fifth conditions) are as described below.

The crystallite size Z is a parameter obtained from the analysis result of the positive electrode active material 100 using XRD, and is calculated using the Scherrer formula (Scherrer) shown in the following formula (6) as described above.

Z＝Kλ/Bcosθ···(6)

( K is the Scherrer constant. Lambda is the wavelength (nm) of the X-rays. B is the width of half-width (°) of the crystallite size. θ is the Bragg angle, i.e. the half value (°) of the diffraction angle 2 θ )

In the case of analyzing the positive electrode active material 100 by XRD, for example, a full-automatic multifunctional X-ray diffraction apparatus SmartLab manufactured by the company corporation is used. In this case, ping Cejiao instrument=smartlab, attachment=standard χcradle, monochromator=bent, scanning mode=2θ/θ, scanning type=ft, X-ray=cukα -ray, irradiation intensity=45 kV/200mA, entrance slit=1/2 deg, light receiving slit 1=1/2 deg, light receiving slit 2=0.300 mm, start=15, stop=90, and step=0.02 are set. With this, in the Scherrer (Scherrer) equation shown in the formula (6), k=0.89, λ (the wavelength of cukα rays) =0.15418 nm, and b=half-width are set.

Specific surface area A (m ² Per g) is the surface area per unit mass of the positive electrode active material 100, and is measured by the BET specific surface area measurement method as described above. The BET specific surface area is measured by bringing nitrogen molecules (N ₂ ) A gas adsorption method in which a plurality of particulate positive electrode active materials 100 are adsorbed, and the specific surface area of the positive electrode active material 100 is measured from the adsorption amount of the nitrogen molecules. In the case of measuring the specific surface area a, for example, a full-automatic specific surface area measuring device Macsorb (registered trademark) manufactured by MOUNTECH co.ltd. In this case, the mass of the positive electrode active material 100 was set to 5g,and the degassing conditions were set at 250℃for 40 minutes.

In the case of analyzing the positive electrode active material 100 using XPS, for example, an X-ray photoelectron spectroscopy analyzer Quantera SXM manufactured by ULVAC-PHI corporation is used. Analysis results of this XPS (C1 s spectrum, O1s spectrum, li1s spectrum, ni2 p) _3/2 Spectrogram, co2p _3/2 Spectrogram, mn2p _1/2 Spectrogram, al2s spectrogram and B1s spectrogram), automatically measuring the intensities of a series of peaks, and then calculating (converting) CO based on the measurement results ₃ Concentration, me-O concentration, li concentration, B concentration, ni concentration, co concentration, mn concentration, and Al concentration. From this, the element concentration ratios R1 to R3 are calculated.

The residual amount of the residual lithium component is measured, for example, by a warder (titration) method. Here, for example, lithium carbonate (Li ₂ CO ₃ ) And lithium hydroxide (LiOH).

In the case of investigating the residual amount, first, a predetermined amount (Sg) of the positive electrode active material 100 is weighed, and then the positive electrode active material 100 is put into a sample bottle. Here, for example, s=10 (g) is set. Next, ultrapure water (50 ml=50 cm) ³ ) The sample was put into a sample bottle together with a stirrer, and then ultrapure water was stirred using a stirrer (stirring time=1 hour). Next, the ultrapure water after stirring was allowed to stand (standing time=1 hour), whereby a supernatant of the ultrapure water was collected using a syringe with filtration, and then the supernatant was filtered. Subsequently, the filtered supernatant (10 ml) was collected using a full-volume pipette, and then, the supernatant was put into a stoppered Erlenmeyer flask.

Subsequently, 1 drop of phenolphthalein solution was added dropwise to the supernatant, and then the supernatant was stirred with a stirrer, followed by titration with a titration solution (hydrochloric acid (HCl) having a concentration of M) until the color of the solution (red) disappeared, whereby the amount of hydrochloric acid added dropwise was read (Aml). Here, for example, the concentration m=0.02 mol/l (=0.02 mol/dm) is set ³ ). Then, two drops of bromophenol blue solution were added dropwise to the supernatant, and the supernatant was stirred with a stirrer while using the aboveThe titration of the solution was performed until the color of the solution changed from blue to yellow-green (blue was lost), and the amount of the hydrochloric acid added dropwise was read (Bml). As the titration apparatus, for example, an automatic titration apparatus COM-1600 manufactured by Pingzhou industries Co., ltd.

Finally, the residual rate (%) of lithium carbonate was calculated using the following formula (7), and the residual rate (%) of lithium hydroxide was calculated using the following formula (8).

Residual ratio (%) = [ (m×2b× (f/1000) ×0.5x 73.892 ×5)/S ] ×100· (7)

( S is the weight (g) of the positive electrode active material 100. A is the amount (ml) of the solution to be added until the end of the first time of using the phenolphthalein solution. B is the amount (ml) of the solution to be added dropwise from the end point of the first time of using the phenolphthalein solution to the end point of the second time of using the bromophenol blue solution. f is a factor dependent on the concentration of the titration solution. M is the concentration (mol/l) of the titration solution )

Residual ratio (%) = [ (m× (a-B) × (f/1000) × 23.941 ×5)/S ] ×100· (8)

Fig. 7 shows a plan view structure corresponding to fig. 5 for explaining the analysis range of XPS and the measurement range of the warder method. However, in fig. 7, only a part of the cover 120 is enlarged together with a part of the positive electrode active material 100 shown in fig. 5, that is, a part of the central portion 110 (one primary particle G1 (G1A)) for simplifying the illustration.

As shown in fig. 7, the range in which the residual lithium component can be analyzed using XPS is only a range near the surface of the positive electrode active material 100, that is, a relatively narrow range F1. In contrast, the range in which the residual lithium component can be measured by the warder method is a relatively wide range F2 from the surface to the inside of the positive electrode active material 100.

[ arbitrary conditions ]

In addition, the positive electrode active material 100 may further satisfy a series of conditions described below.

Specifically, the specific surface area A is preferably 0.53m ² /g～1.25m ² And/g. This is because the decomposition reaction of the electrolyte is sufficiently suppressed, and the generation of gas is also sufficiently suppressed.

The particle size of the volume-based particle size distribution is not particularly limited. Among them, the particle diameter D50 is preferably 11.8 μm to 14.4. Mu.m. In this case, the particle diameter D10 is preferably 2.8 μm to 4.0 μm, and the particle diameter D90 is preferably 22.7 μm to 26.3. Mu.m. This is because the occurrence of short-circuiting and the peeling of the positive electrode active material layer 21B can be suppressed while securing energy density per unit weight. These particle diameters can be measured, for example, using a laser diffraction particle size distribution measuring apparatus SALD-2100 manufactured by Shimadzu corporation.

Specifically, if the particle diameter is too small, the positive electrode active material layer 21B is easily peeled from the positive electrode current collector 21A when the positive electrode active material layer 21B is compression molded in the production of the positive electrode 21. In addition, since the surface area of the positive electrode active material 100 increases, the addition amount of the conductive agent, the binder, and the like must be increased, and thus the energy density per unit weight is easily lowered. On the other hand, if the particle diameter is too large, the positive electrode active material 100 is likely to penetrate the separator 23, and the positive electrode 21 and the negative electrode 22 are likely to be short-circuited.

In the case where the above-mentioned condition concerning the particle diameter of the volume-based particle size distribution is satisfied, the compressed density is preferably 3.40g/cm ³ ～3.60g/cm ³ . This is because the generation of gas can be suppressed while ensuring a high energy density.

In detail, if the compressed density is less than 3.40g/cm ³ The positive electrode 21 (positive electrode active material layer 21B) is not easily filled with the positive electrode active material 100, and therefore the energy density per unit weight is easily reduced. On the other hand, if the compressed density is more than 3.60g/cm ³ The positive electrode active material 100 is easily broken, and a new surface having reactivity is formedGas is easily generated.

The compressed density (g/cm) ³ ) The measurement is performed, for example, according to the procedure described below. First, the positive electrode active material 100 and cellulose were put into a mortar, and then the positive electrode active material 100 and cellulose were uniformly mixed using the mortar, whereby a mixed sample was obtained. In this case, the mixing ratio (weight ratio) was set to 100:cellulose=98:2 as the positive electrode active material. Subsequently, 1g of the mixed sample was measured, and then the mixed sample was punched with a punching jig under a constant pressure (punching pressure=60 MPa), thereby obtaining a sample having a predetermined area (cm) ² ) The mixed sample was molded in the form of pellets. Then, the thickness (cm) of the mixed sample was measured. In this case, the thicknesses are measured for five portions different from each other, and then the average value of the thicknesses of the five portions is calculated. Then, the weight (g) of the mixed sample was measured. Finally, from the measurement results of the thickness and the weight, the compression density=weight/(area×thickness) is calculated.

Further, it is preferable that the positive electrode active material 100 having two or more average particle diameters is used, so that the volume-based particle size distribution of the positive electrode active material 100 has two or more peaks. This is because the positive electrode 21 (positive electrode active material layer 21B) is easier to fill with the positive electrode active material 100 than in the case where the volume-based particle size distribution has only one peak. In addition, this is because the number of contact points between the positive electrode active materials 100 is increased, and thus the force during compression molding is easily dispersed during the production of the positive electrode 21 (during compression molding of the positive electrode active material layer 21B), and the positive electrode active material 100 is less likely to break. Thereby, the energy density per unit weight increases. In addition, since the decomposition reaction of the electrolyte solution due to the formation of the new surface having reactivity can be suppressed, the generation of gas due to the decomposition reaction of the electrolyte solution can also be suppressed. The volume-based particle size distribution can be measured by using the laser diffraction particle size distribution measuring apparatus described above, for example.

Fig. 8 shows an example of the volume-based particle size distribution. In fig. 8, the horizontal axis represents particle diameter (μm), and the vertical axis represents relative particle amount (%). As shown in fig. 8, in the case where the volume-based particle size distribution has two peaks P (P1, P2) (a two-particle mixed system), it is preferable that the volume-based particle size distribution has a first peak P1 (first peak) in a range Q1 having a particle diameter of 3 μm to 7 μm and a second peak P2 (second peak) in a range Q2 having a particle diameter of 14 μm to 30 μm. This is because, when the particle diameters (D10, D50, D90) of the volume-based particle size distribution satisfy the above-described conditions, the positive electrode 21 (positive electrode active material layer 21B) tends to have a densely packed structure in the positive electrode active material 100. In fig. 8, the ranges Q1 and Q2 are hatched, respectively.

In the case where the condition concerning the particle diameters of the two peaks P (P1, P2) of the above-mentioned volume-based particle size distribution is satisfied, the compression density is preferably 3.45g/cm ³ ～3.70g/cm ³ . This is because the generation of gas can be suppressed while ensuring a high energy density for the same reason as in the case where the condition concerning the particle diameter of the volume-based particle size distribution is satisfied.

<1-2 action >

In this secondary battery 10, for example, at the time of charging, lithium ions are deintercalated from the positive electrode 21 (positive electrode active material layer 21B), and the lithium ions are intercalated into the negative electrode 22 (negative electrode active material layer 22B) via the electrolyte. In addition, in the secondary battery 10, for example, at the time of discharge, lithium ions are deintercalated from the negative electrode 22, and the lithium ions are intercalated into the positive electrode 21 via the electrolyte.

The open circuit voltage (i.e., the battery voltage) in the fully charged state of each pair of electrodes (positive electrode 21 and negative electrode 22) is not particularly limited, and may be less than 4.20V or more. Among them, the battery voltage is preferably 4.25V or more, more preferably 4.25V to 6.00V. This is because the amount of lithium released per unit mass increases even when the same kind of positive electrode active material is used, as compared with the case where the battery voltage is 4.20V. In this case, in order to obtain a high energy density, the amount of the positive electrode active material and the amount of the negative electrode active material are adjusted to each other in accordance with the amount of lithium deintercalation per unit mass.

<1-3. Method of production >

Hereinafter, a method for manufacturing the positive electrode active material 100 will be described with reference to fig. 5, and a method for manufacturing the secondary battery 10 using the positive electrode active material 100 will be described with reference to fig. 1 to 4.

<1-3-1. Method for producing positive electrode active material >

In the case of manufacturing the positive electrode active material 100, for example, as described below, the precursor manufacturing process, the first baking process, the water washing process, and the covering process (second baking process) are sequentially performed in this order.

[ procedure for producing precursor ]

First, as a raw material, a supply source of lithium (lithium compound), a supply source of nickel (nickel compound), and a supply source of an additional metal element (M shown in formula (1)) prepared as needed (additional compound) are prepared. In the following, for example, a case of using an additional compound (additional metal element) will be described. The lithium compound may be, for example, an inorganic compound or an organic compound. The lithium compound may be one kind or two or more kinds. Here, the description is given of the lithium compound, and the nickel compound and the additional compound are the same.

Specific examples of the lithium compound are as follows. Examples of the lithium compound as the inorganic compound include lithium hydroxide, lithium carbonate, lithium nitrate, lithium fluoride, lithium chloride, lithium bromide, lithium iodide, lithium chlorate, lithium perchlorate, lithium bromate, lithium iodate, lithium oxide, lithium peroxide, lithium sulfide, lithium bisulfide, lithium sulfate, lithium bisulfide, lithium nitride, lithium azide, lithium nitrite, lithium phosphate, lithium dihydrogen phosphate, and lithium bicarbonate. Examples of the lithium compound as the organic compound include methyllithium, vinyllithium, isopropyllithium, butyllithium, phenyllithium, lithium oxalate, and lithium acetate.

Then, the nickel compound and the additional compound are dissolved using an aqueous solvent such as pure water, and then a coprecipitate (nickel composite coprecipitated hydroxide) is obtained by a coprecipitation method. In this case, according to the finalThe composition of the obtained center portion 110 (lithium nickel composite oxide) was adjusted to adjust the mixing ratio of the nickel compound and the additional compound. As the alkali compound for coprecipitation, sodium hydroxide (NaOH) and ammonium hydroxide (NH) are used, for example ₄ OH), and the like. Next, the nickel composite coprecipitated hydroxide is washed with water, and then the nickel composite coprecipitated hydroxide is dried.

Here, as described above, in the case of using two types of positive electrode active materials 100 (Bi-model design composed of large-particle-diameter particles and small-particle-diameter particles) having different particle diameters, when a nickel composite coprecipitated hydroxide is obtained by the coprecipitation method, the particle diameter of the secondary particles G2 of the nickel composite coprecipitated hydroxide is adjusted by adjusting the reaction time at the coprecipitation. Thus, nickel composite co-precipitated hydroxides (large particle diameter particles) having a relatively large desired average particle diameter and nickel composite co-precipitated hydroxides (small particle diameter particles) having a relatively small desired average particle diameter are obtained.

Finally, a lithium compound, a nickel composite coprecipitated hydroxide and an optional additional compound are mixed to obtain a precursor. In this case, the mixing ratio of the nickel compound, the nickel composite co-precipitated hydroxide and the additional compound is adjusted according to the composition of the finally obtained central portion 110 (lithium nickel composite oxide).

In the precursor production step, the specific surface area a can be controlled by adjusting the particle size of the secondary particles G2 of the nickel composite co-precipitated hydroxide.

[ first firing step ]

The precursor containing the additional compound together with the lithium compound and the nickel composite coprecipitated hydroxide is calcined as necessary. Thus, a compound (lithium-nickel composite oxide) containing lithium, nickel, and additional metal elements as constituent elements is formed, and thus the center portion 110 containing the lithium-nickel composite oxide is obtained. In the lithium nickel composite oxide obtained here, most of the plurality of primary particles G1 are aggregated, and therefore most of the plurality of primary particles G1 form secondary particles G2.

The conditions such as the baking temperature are not particularly limited, and thus can be arbitrarily set. Among them, the baking temperature is preferably 650 to 850 ℃. This is because a lithium nickel composite oxide having a stable composition can be easily produced with good reproducibility.

In detail, if the firing temperature is less than 650 ℃, the lithium compound is not easily diffused, and the crystal structure of the R3m layered rock salt is not easily formed sufficiently. On the other hand, if the firing temperature is higher than 850 ℃, defects in lithium due to volatilization of the lithium compound tend to occur in the crystal structure of the lithium nickel composite oxide, and the composition of the lithium nickel composite oxide tends to become non-stoichiometric due to incorporation of other atoms into the defective sites (empty sites) of the lithium. The other atoms being, for example, those having a structure similar to lithium (Li ⁺ ) Nickel (Ni) ²⁺ ) Etc.

In addition, if nickel is incorporated into the lithium 3d site, the nickel incorporation region becomes a cubic halite phase (halite domain). The electrochemistry of the rock salt domain is inert and nickel incorporated into the lithium site has the property of readily impeding solid phase diffusion of the lithium separate phase. This tends to induce a decrease in battery characteristics (including resistance characteristics) of the secondary battery 10.

In addition, in the firing of the precursor, it is preferable to fire the precursor in an oxygen atmosphere in order to suppress the occurrence of an unnecessary reduction reaction. The reduction reaction is, for example, a reduction reaction of nickel (Ni ³⁺ →Ni ²⁺ ) Etc.

In the first firing step, the specific surface area a and the crystallite size Z can be controlled by adjusting the firing temperature.

[ washing step ]

The center portion 110 (lithium nickel composite oxide) is cleaned using an aqueous solvent such as pure water. In this case, the central portion 110 may be mechanically cleaned using a stirrer or the like, as necessary. The conditions such as the cleaning time are not particularly limited, and thus can be arbitrarily set.

In this washing step, the element concentration ratios R1 and R2 can be controlled by adjusting the washing time, and thus the residual amount of the residual lithium component can be controlled.

[ covering step (second baking step) ]

A boron compound is mixed with the central portion 110 (lithium nickel composite oxide), and then the mixture is baked. In this case, the mixing ratio of the center portion 110 and the boron compound is adjusted so that the amount of boron present (the coating amount) on the surface of the center portion 110 becomes a desired value. Thereby, the boron compound is fixed to the surface of the central portion 110, so that the surface of the central portion 110 is covered with the boron compound, and thus the covering portion 120 containing the boron compound is formed. Accordingly, the positive electrode active material 100 including the central portion 110 (lithium nickel composite oxide) and the covering portion 120 (boron compound) can be obtained.

In this coating step (second baking step), the element concentration ratio R3 can be controlled by adjusting the amount of the boron compound added, and thus the coating state of the surface of the lithium nickel composite oxide by the boron compound can be controlled. In addition, by adjusting the baking temperature, the element concentration ratios R1 and R2 can be controlled.

<1-3-2. Method for manufacturing secondary battery >

In the case of manufacturing the secondary battery 10, for example, as described below, the manufacturing process of the positive electrode 21, the manufacturing process of the negative electrode 22, the manufacturing process of the electrolyte, and the assembling process of the secondary battery 10 are sequentially performed.

[ production Process of Positive electrode ]

First, the positive electrode active material 100, a binder, and a conductive agent are mixed to prepare a positive electrode mixture. Next, a paste-like positive electrode mixture slurry is prepared by dispersing the positive electrode mixture in a dispersing solvent. The type of the solvent for dispersion is not particularly limited, but is, for example, an organic solvent such as N-methyl-2-pyrrolidone. Next, a positive electrode mixture slurry is applied to both surfaces of the positive electrode current collector 21A (positive electrode active material layer forming portion 21M), thereby forming a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B is compression molded using a roll press. Thus, the positive electrode 21 is produced by forming the positive electrode active material layer 21B on both sides of the positive electrode current collector 21A.

[ procedure for producing negative electrode ]

First, a negative electrode active material, a binder, and a conductive agent are mixed to prepare a negative electrode mixture. Next, a paste-like negative electrode mixture slurry is prepared by dispersing the negative electrode mixture in a dispersing solvent. The type of the solvent for dispersion is not particularly limited, but is, for example, an organic solvent such as N-methyl-2-pyrrolidone or methyl ethyl ketone. Next, the negative electrode active material layer 22B is formed by applying a negative electrode mixture slurry to both surfaces of the negative electrode current collector 22A (negative electrode active material layer forming portion 22M). Finally, the anode active material layer 22B is compression molded using a roll press. Thus, the anode 22 is fabricated by forming the anode active material layer 22B on both sides of the anode current collector 22A.

[ procedure for producing electrolyte ]

Electrolyte salt is added to the solvent, and then the solvent is stirred. Thus, an electrolyte solution is prepared since the electrolyte salt is dissolved by the solvent.

[ assembling Process of Secondary Battery ]

First, a plurality of positive electrodes 21 and a plurality of negative electrodes 22 are alternately laminated with separators 23 interposed therebetween, thereby forming a laminate. Next, the plurality of positive electrode current collector exposure portions 21N are bonded to each other, and the positive electrode lead 11 is bonded to the bonded plurality of positive electrode current collector exposure portions 21N. In addition, the plurality of anode current collector exposure portions 22N are bonded to each other, and the anode lead 12 is bonded to the bonded plurality of anode current collector exposure portions 22N. The method of bonding the positive electrode lead 11 and the negative electrode lead 12 is not particularly limited, but is, for example, ultrasonic welding, resistance welding, brazing, or the like.

Next, the laminated body is arranged between the first member 30A and the second member 30B, and then the first member 30A and the second member 30B are overlapped with each other with the laminated body interposed therebetween. Next, the outer peripheral edge portions of the remaining three sides of each of the first member 30A and the second member 30B, excluding the outer peripheral edge portion of one side, are brought into close contact with each other, whereby the laminate is accommodated in the bag-shaped outer package member 30. The method of adhering the first member 30A and the second member 30B to each other is not particularly limited, and for example, a hot-melt method or an adhesive may be used.

Finally, the electrolyte is injected into the bag-shaped outer package member 30, and then the outer peripheral edge portions of the remaining sides of the first member 30A and the second member 30B are brought into close contact with each other, thereby sealing the outer package member 30. In this case, the sealing film 13 is interposed between the outer package member 30 (the first member 30A and the second member 30B) and the positive electrode lead 11, and the sealing film 13 is interposed between the outer package member 30 and the negative electrode lead 12. The adhesive film 13 may be attached to the positive electrode lead 11 and the negative electrode lead 12, respectively, in advance. Thus, the electrolyte is impregnated into the laminate, thereby forming the electrode body 20. In addition, the electrode body 20 is housed in the outer package member 30, and the positive electrode lead 11 and the negative electrode lead 12 are led out from the inside of the outer package member 30, whereby the secondary battery 10 is assembled. Accordingly, the laminated film type secondary battery 10 is completed.

<1-4. Actions and Effect >

In this secondary battery 10, the positive electrode 21 has a positive electrode active material 100, and the positive electrode active material 100 includes a central portion 110 (lithium nickel composite oxide) and a coating portion 120 (boron compound), and the structure and physical properties of the positive electrode active material 100 satisfy the five conditions (first to fifth conditions) described above. In this case, as described above, the generation of gas can be suppressed while suppressing the decomposition reaction of the electrolyte while ensuring the input and output of lithium ions. Accordingly, even if charge and discharge are repeated, the discharge capacity is not easily lowered and the secondary battery 10 is not easily expanded, so that excellent battery characteristics can be obtained.

In particular, if the specific surface area A of the positive electrode active material 100 is 0.53m ² /g～1.25m ² In the case of the composition of the present invention, the electrolyte solution is sufficiently suppressed in the decomposition reaction and the generation of gas is sufficiently suppressed, and thus a higher effect can be obtained.

In addition, when the particle diameter D50 of the particle size distribution based on the volume of the positive electrode active material 100 is 11.8 μm to 14.4 μm, the occurrence of short-circuiting and peeling of the positive electrode active material layer 21B can be suppressed while securing the energy density per unit weight, becauseThis can give a higher effect. In this case, if the particle diameter D10 is 2.8 μm to 4.0 μm and the particle diameter D90 is 22.7 μm to 26.3. Mu.m, further higher effects can be obtained. In addition, if the compressed density of the positive electrode active material 100 is 3.40g/cm ³ ～3.60g/cm ³ The generation of gas can be suppressed while securing a high energy density, and thus a higher effect can be obtained.

In addition, if the volume-based particle size distribution of the positive electrode active material 100 has two or more peaks, the positive electrode 21 (positive electrode active material layer 21B) is more likely to be filled with the positive electrode active material 100 and less likely to be broken, so that the energy density per unit weight can be increased and the decomposition reaction of the electrolyte and the generation of gas can be suppressed, thereby obtaining a higher effect. In this case, if the volume-based particle size distribution has two peaks (a peak having a particle diameter in the range of 3 μm to 7 μm and a peak having a particle diameter in the range of 14 μm to 30 μm), the positive electrode active material 100 is likely to have a densely packed structure, and thus a further high effect can be obtained. In addition, if the compressed density of the positive electrode active material 100 is 3.45g/cm ³ ～3.70g/cm ³ The generation of gas can be suppressed while securing a high energy density, and thus a higher effect can be obtained.

In addition, if the positive electrode 21, the negative electrode 22, and the electrolyte are contained in the film-shaped outer packaging member 30, the gas generation can be suppressed in the laminated film-type secondary battery 10 using the outer packaging member 30 that is easily deformed due to the change in the internal pressure, as described above. Thus, even when the laminated film type secondary battery 10 in which the swelling is easily made remarkable is used, the swelling of the secondary battery 10 can be effectively suppressed.

In addition, the positive electrode active material 100 for the secondary battery 10 includes a central portion 110 (lithium nickel composite oxide) and a covering portion 120 (boron compound), and the structure and physical properties of the positive electrode active material 100 satisfy the five conditions described above. For the above reasons, the structure and physical properties of the positive electrode active material 100 are optimized, and therefore, excellent battery characteristics can be obtained in the secondary battery 10 using the positive electrode active material 100.

<2 > modification example

The structure of the secondary battery 10 described above can be appropriately modified as described below. Further, a series of modifications described below may be combined with any two or more of them.

Modification 1

As shown in fig. 1, two outer package members 30 (a first member 30A and a second member 30B) are used. However, as shown in fig. 9 corresponding to fig. 1, instead of two outer package members 30, one outer package member 30 that can be folded may be used. The one outer package member 30 has a structure in which, for example, one side of the first member 30A and one side of the second member 30B opposite to the first member 30A are connected to each other. In this case, the electrode body 20 is housed in the outer package member 30, and thus the same effect can be obtained.

Modification 2

An electrolyte solution is used as the liquid electrolyte. However, an electrolyte layer as a gel-like electrolyte may be used instead of the electrolyte solution. In this case, the electrode body 20 includes an electrolyte layer, and the plurality of positive electrodes 21 and the plurality of negative electrodes 22 are alternately laminated with the electrolyte layer interposed between the separator 23 and the electrode body 20. The electrolyte layer is interposed between the positive electrode 21 and the separator 23, and between the negative electrode 22 and the separator 23. The electrolyte layer contains an electrolyte solution and a polymer material that holds the electrolyte solution, and the polymer material is swelled by the electrolyte solution. The gel electrolyte can obtain high ionic conductivity and inhibit leakage of electrolyte. In addition, the mixing ratio of the electrolyte to the polymer material can be arbitrarily set. The polymer material may be, for example, a homopolymer such as polyvinylidene fluoride, a copolymer such as a copolymer of vinylidene fluoride and hexafluoropropylene, or both. In this case, since lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer, the same effect can be obtained.

Modification 3

The separator 23 may include, for example, a base material layer and a polymer layer provided on the base material layer. The polymer layer may be provided on only one side of the base material layer, or may be provided on both sides of the base material layer.

The substrate layer is, for example, the porous film described above. The polymer layer includes, for example, a polymer material such as polyvinylidene fluoride. This is because the physical strength is excellent and the electrochemical properties are stable. The polymer layer may contain a plurality of inorganic particles, for example. This is because, when the secondary battery 10 is high Wen Huashi due to heat generation or the like, heat is released by a plurality of inorganic particles, and the safety of the secondary battery 10 is improved. The type of the inorganic particles is not particularly limited, but is, for example, insulating particles such as alumina and aluminum nitride. The separator 23 including the base material layer and the polymer layer is formed by, for example, coating a precursor solution including a polymer material, an organic solvent, and the like on both sides of the base material layer.

In this case, the positive electrode 21 and the negative electrode 22 are separated from each other with the separator 23 interposed therebetween, and therefore the same effect can be obtained. In the case where the separator 23 includes a polymer layer, the electrolyte layer may be omitted. This is because the polymer layer swelled with the electrolyte solution is made to perform the same function as the electrolyte layer by impregnating the polymer layer with the electrolyte solution.

Modification 4

A laminated electrode body 20 in which a plurality of positive electrodes 21 and a plurality of negative electrodes 22 are alternately laminated with separators 23 is used, but the structure of the electrode body 20 is not particularly limited. Specifically, the electrode body 20 may be, for example, a folded type in which a single positive electrode 21 and a single negative electrode 22 are folded with a separator 23 interposed therebetween, or a wound type in which a single positive electrode 21 and a single negative electrode 22 are wound with a separator 23 interposed therebetween. In these cases, since the positive electrode 21 and the negative electrode 22 can be charged and discharged, the same effect can be obtained.

<3 > use of secondary cell

The use of the secondary battery is not particularly limited as long as the secondary battery can be used as a power source for driving, a power storage source for storing electric power, and other machines, devices, appliances, devices, systems (an aggregate of a plurality of devices, and the like), and the like. The secondary battery used as the power source may be a main power source or an auxiliary power source. The main power supply is a power supply that is preferentially used regardless of the presence or absence of other power supplies. The auxiliary power supply may be a power supply used in place of the main power supply, or may be a power supply that is switched from the main power supply as needed. In the case of using the secondary battery as the auxiliary power source, the kind of the main power source is not limited to the secondary battery.

Specifically, the secondary battery is used, for example, as follows. Examples of such electronic devices include video cameras, digital cameras, mobile phones, notebook personal computers, cordless phones, stereo headphones, portable radios, portable televisions, and portable information terminals (including portable electronic devices). Is a portable living appliance such as an electric shaver and the like. Is a storage device such as a standby power supply and a memory card. Is an electric tool such as an electric drill, an electric saw and the like. A battery pack mounted on a notebook personal computer or the like as a detachable power source. Is used for medical electronic instruments such as pacemakers, hearing aids and the like. Is an electric vehicle such as an electric vehicle (including a hybrid vehicle). A power storage system such as a household battery system that stores electric power in advance for emergency. Of course, the secondary battery may be used in applications other than the above.

Examples

Embodiments of the present technology are described. The procedure of the description is as follows.

1. Synthesis of positive electrode active material

2. Fabrication of secondary battery

3. Evaluation of Battery characteristics

4. Derivation theory of proper range of specific surface area

5. Inspection of

6. Other evaluations and review

7. Summary.

Experimental example 1-1 to 1-23

As described below, the positive electrode active material 100 shown in fig. 5 was synthesized, and the secondary battery 10 of the laminated film type shown in fig. 1 to 4 was produced, and then the physical properties of the positive electrode active material 100 and the battery characteristics of the secondary battery 10 were evaluated.

<1 > Synthesis of Positive electrode active Material >

In the precursor production step, first, a nickel compound (nickel sulfate (NiSO) ₄ ) And additional compounds (cobalt sulfate (CoSO) ₄ ) Then, the aqueous solvent is stirred, thereby obtaining a mixed aqueous solution. In this case, the mixing ratio of the nickel compound and the cobalt compound was adjusted so that the molar ratio of nickel to cobalt was nickel to cobalt=84:16.

Subsequently, the mixed aqueous solution is stirred, and an alkali compound (lithium hydroxide (NaOH) and ammonium hydroxide (NH) are added to the mixed aqueous solution ₄ OH)), thereby obtaining a plurality of granular precipitates (secondary particles G2 of nickel cobalt composite coprecipitated hydroxide) by the coprecipitation method. In this case, in order to finally use the positive electrode active material 100 (Bi-model design composed of large particle diameter particles and small particle diameter particles) having two average particle diameters (median particle diameter), the particle diameters of the secondary particles G2 are controlled, thereby obtaining secondary particles G2 having two average particle diameters different from each other.

Next, the nickel-cobalt composite co-precipitated hydroxide is washed with an aqueous solvent (pure water), and then dried.

Finally, a lithium compound (lithium hydroxide monohydrate (lioh.h) ₂ O)) and additional compounds (aluminum hydroxide (Al (OH)) ₃ ) Thus, a precursor was obtained. In this case, the mixing ratio of the nickel-cobalt composite coprecipitated hydroxide, the lithium compound and the additional compound is adjusted so that the molar ratio of lithium to nickel to cobalt to aluminum is lithium (nickel+cobalt+aluminum) =103:100.

In the first firing step, the precursor is fired in an oxygen atmosphere. The firing temperature (. Degree. C.) in the first firing step is shown in Table 1. Thus, a plurality of particulate lithium nickel composite oxides (LiNi _0.82 Co _0.14 Al _0.04 O ₂ ) Thus, the center portion 110 including the lithium nickel composite oxide was obtained.

In the water washing step, first, the volume of 1000ml (=1000 cm) ³ ) In the beaker of (a),50g of the center portion 110 and 500ml (=500 cm) of an aqueous solvent (pure water) were charged ³ ). Next, the aqueous solvent is stirred by a stirrer, and the central portion 110 is washed with the aqueous solvent. The washing time (minutes) is shown in table 1. Next, the aqueous solvent was transferred to a suction filter, and then the filtrate was dehydrated (dehydration time=10 minutes). Next, the filtrate was dried (drying temperature=120℃). Next, the filtrate was pulverized using an agate mortar, and then the pulverized product was vacuum-dried (drying time=100 ℃). Thus, the center portion 110 after washing with water is obtained.

In the covering step (second baking step), the center portion 110 is covered with a boron compound (boric acid (H) ₃ BO ₃ ) Mixing, thereby obtaining a mixture. The amount of boric acid added (mass%), i.e., the ratio of the mass of boric acid to the mass of the center portion 110, is shown in table 1. The mixture is then calcined in an oxygen atmosphere. The firing temperature (. Degree. C.) in the second firing step is shown in Table 1. Thus, as shown in fig. 5, the surface of the central portion 110 (lithium nickel composite oxide) is covered with the covering portion 120 (boron compound), thereby obtaining the positive electrode active material 100.

As shown in table 1, other lithium nickel composite oxides in the form of a plurality of particles were synthesized, and thus, other positive electrode active materials 100 were also obtained.

Specifically, liNi was synthesized by changing the molar ratio of lithium, nickel, cobalt, and aluminum _0.78 Co _0.18 Al _0.04 O ₂ And LiNi _0.90 Co _0.06 Al _0.04 O ₂ Instead of LiNi _0.82 Co _0.14 Al _0.04 O ₂ Other positive electrode active material 100 was obtained by the same procedure except for this.

In addition, manganese hydroxide (Mn (OH) ₂ ) As an additional compound to replace aluminum hydroxide and adjusting the mole ratio of lithium, nickel, cobalt and manganese, liNi was synthesized _0.84 Co _0.08 Mn _0.08 O ₂ Instead of LiNi _0.82 Co _0.14 Al _0.04 O ₂ In addition to that, lead toOther positive electrode active materials 100 were obtained by the same procedure.

TABLE 1

The positive electrode active material 100 was analyzed by XRD, and then, the crystallite size Z (nm) was calculated from the analysis result ((peak of 104) crystal plane) using Scherrer's formula, and the results shown in table 2 and table 3 were obtained. The specific surface area a (m) of the positive electrode active material 100 was measured by BET specific surface area measurement ² And/g) were measured, and the results shown in Table 2 and Table 3 were obtained. Further, the "suitable ranges (m ² And/g) "represents an appropriate range of the specific surface area A derived from the formula (2). Namely, "proper range (m ² Of the two values shown in the column of/g), the value on the left is the value calculated from-0.0160 xz+1.72, while the value on the right is the value calculated from-0.0324 xz+2.94.

Further, the positive electrode active material 100 was analyzed by XPS, and then, the element concentration ratios R1 to R3 were calculated from the analysis results, and the results shown in table 2 and table 3 were obtained.

TABLE 2

TABLE 3

In addition, the compressed density of the positive electrode active material 100 was measured, and as a result, the compressed density was 3.60g/cm ³ . As a result of measuring the particle size of the volume-based particle size distribution of the positive electrode active material 100, the particle size d50=13.2 μm, the particle size d10=3.4 μm, and the particle size d90=24.5 μm.

As a result of measuring the volume-based particle size distribution of the positive electrode active material 100, two peaks P are obtained, i.e., a peak P1 corresponding to small-sized particles and a peak P2 corresponding to large-sized particles, as shown in fig. 8. In this volume-based particle size distribution, the particle diameter corresponding to the first peak P1 (the particle diameter of the peak top) is 4.4 μm, and the particle diameter corresponding to the second peak P2 is 19.1 μm. Further, the mixing ratio (weight ratio) of the small particle diameter particles and the large particle diameter particles was set to be small particle diameter particles: large particle diameter particles=30:70.

<2 > production of secondary cell

In the process of producing the positive electrode 21, first, 95.5 parts by mass of the positive electrode active material 100 (the center portion 110 and the cover portion 120), 1.9 parts by mass of the binder (polyvinylidene fluoride), 2.5 parts by mass of the conductive agent (carbon black), and 0.1 parts by mass of the dispersing agent (polyvinylpyrrolidone) are mixed to prepare a positive electrode mixture. Next, a positive electrode mixture was poured into an organic solvent (N-methyl-2-pyrrolidone), and then the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. Next, a positive electrode mixture slurry was applied to both surfaces of the positive electrode active material layer forming portion 21M in the positive electrode current collector 21A (aluminum foil, thickness=15 μm) using an application device, and then the positive electrode mixture slurry was dried, thereby forming the positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B is compression molded using a roll press.

In the process of producing the negative electrode 22, first, 90 parts by mass of a negative electrode active material (graphite) and 10 parts by mass of a binder (polyvinylidene fluoride) are mixed to prepare a negative electrode mixture. Next, a negative electrode mixture was poured into an organic solvent (N-methyl-2-pyrrolidone), and then the organic solvent was stirred, whereby a paste-like negative electrode mixture slurry was prepared. Next, a negative electrode mixture paste was applied to both surfaces of the negative electrode active material layer forming portion 22M in the negative electrode current collector 22A (copper foil, thickness=15 μm) using an applicator, and then the negative electrode mixture paste was dried, thereby forming the negative electrode active material layer 22B. Finally, the anode active material layer 22B is compression molded using a roll press.

In the step of preparing the electrolyte, an electrolyte salt (lithium hexafluorophosphate) is added to a solvent (ethylene carbonate and methylethyl carbonate), and then the solvent is stirred. In this case, the mixing ratio (mass ratio) of the solvent was made to be ethylene carbonate to methylethyl carbonate=50:50, and the content of the electrolyte salt was made to be 1mol/kg with respect to the solvent.

In the assembly process of the secondary battery 10, first, a plurality of positive electrodes 21 and a plurality of negative electrodes 22 are alternately laminated with separators 23 (microporous polyethylene film, thickness=25 μm) interposed therebetween, thereby forming a laminate. Next, the plurality of positive electrode current collector exposed portions 21N are joined to each other and the plurality of negative electrode current collector exposed portions 22N are joined to each other by ultrasonic welding. Next, the positive electrode lead 11 is joined to the joined body of the plurality of positive electrode current collector exposed portions 21N and the negative electrode lead 12 is joined to the joined body of the plurality of negative electrode current collector exposed portions 22N by ultrasonic welding.

Next, two outer package members 30 (a first member 30A and a second member 30B) are prepared. As the exterior package member 30, a moisture-proof aluminum laminate film in which a heat-seal resin layer (polypropylene film, thickness=30 μm), a metal layer (aluminum foil, thickness=40 μm), and a surface protective layer (nylon film, thickness=25 μm) are laminated in this order was used. Next, a laminate is disposed between the first member 30A and the second member 30B, and then the outer peripheral edge portions of the three sides of each of the first member 30A (heat-welded resin layer) and the second member 30B (heat-welded resin layer) are brought into close contact with each other by a heat welding method, whereby the laminate is accommodated in the interior of the bag-shaped outer package member 30.

Finally, an electrolyte is injected into the bag-shaped exterior packaging member 30, and then the exterior packaging member 30 is sealed by a thermal welding method. In this case, the sealing film 13 (polypropylene film, thickness=15 μm) is interposed between the outer packaging member 30 (first member 30A and second member 30B) and the positive electrode lead 11, and the sealing film 13 is interposed between the outer packaging member 30 and the negative electrode lead 12. Thus, the electrolyte is impregnated into the laminate, thereby forming the electrode body 20. The electrode body 20 is housed in the outer package member 30 while the positive electrode lead 11 and the negative electrode lead 12 are led out from the inside of the outer package member 30. Accordingly, the secondary battery 10 of the laminated film type shown in fig. 1 to 4 is completed.

<3. Evaluation of Battery characteristics >

The battery characteristics of the secondary battery 10 were evaluated, and the results shown in tables 2 and 3 were obtained. Here, as battery characteristics of the secondary battery 10, initial capacity characteristics and cycle characteristics were investigated, and gas generation characteristics were investigated in order to investigate physical properties of the positive electrode active material 100. In this case, the residual lithium components were also investigated together by the above steps (lithium carbonate (Li ₂ CO ₃ ) And lithium hydroxide (LiOH)).

In order to examine the primary capacity characteristics of the secondary battery 10, first, the secondary battery 10 was charged and discharged once in a normal temperature environment (temperature=23℃) in order to stabilize the state of the secondary battery 10. Thereafter, the secondary battery 10 was again charged and discharged in the same environment, and the initial capacity (discharge capacity in the second cycle) was measured. The primary capacities shown in tables 2 and 3 are normalized values in which the primary capacity of experimental example 1-1 is set to 100.

In the charging, the constant current charging was performed at a current of 0.1C until the battery voltage reached 4.2V, and then the constant voltage charging was performed at the battery voltage of 4.2V until the current reached 0.005C. At the time of discharging, constant current discharge was performed at a current of 0.1C until the battery voltage reached 2.5V. Further, 0.1C means a current value at which the battery capacity (theoretical capacity) is completely discharged at 10 hours, and 0.005C means a current value at which the battery capacity is completely discharged at 200 hours.

In the case of investigating the cycle characteristics of the secondary battery 10, the state of the secondary battery 10 was stabilized by the above-described procedure, and then, first, the secondary battery 10 was subjected to charge and discharge cycles in a high-temperature environment (temperature=60 ℃) once, and the discharge capacity (the discharge capacity of the second cycle) was measured. Next, the discharge capacity (discharge capacity at 102 th cycle) was measured by cycling the secondary battery 10 for 100 times in the same environment. Finally, a capacity maintenance ratio (%) = (discharge capacity of 102 th cycle/discharge capacity of second cycle) ×100 was calculated.

In charging, constant current charging was performed at a current of 1.0C until the battery voltage reached 4.2V, and then constant voltage charging was performed at the battery voltage of 4.2V until the total charging time reached 2.5 hours. At the time of discharging, constant current discharge was performed at a current of 5.0C until the battery voltage reached 2.5V. Further, 1.0C means a current value at which the battery capacity is completely discharged in 1 hour, and 5.0C means a current value at which the battery capacity is completely discharged in 0.2 hour.

In order to examine the gas generation characteristics of the positive electrode active material 100, first, the positive electrode 21 and the negative electrode 22 were laminated with the separator 23 interposed therebetween, whereby a laminate was obtained. Then, the laminated film having the tab attached in advance so as to be chargeable and dischargeable is folded, and then a laminate is interposed between the folded laminated films. Next, the outer peripheral edge portions of both sides of the laminated film are heat-welded to each other, whereby the laminate is accommodated inside the bag-like laminated film. Next, an electrolyte is injected into the inside of the bag-shaped laminated film, and then the outer peripheral edge portions of the remaining one side of the laminated film are thermally welded to each other, thereby obtaining a laminated package. Next, the laminated package was pressurized (pressure=500 kP, pressurization time=30 seconds). Thus, the laminate was impregnated with the electrolyte solution, and thus, a laminated cell for evaluation was produced.

Then, the laminated cell for evaluation was charged (constant current charge) with a current of 0.1C until the voltage reached 4.2V, and the laminated cell for evaluation was charged (constant voltage charge) with the voltage of 4.2V until the total charging time reached 2.5 hours, and then the volume of the laminated cell for evaluation (volume before storage: cm) was measured by the Archimedes method ³ ) The measurement was performed. Next, the laminated cell for evaluation in a charged state was stored (storage time=one week) in a constant temperature bath (temperature=60 ℃), and then the volume (volume after storage) of the laminated cell for evaluation was measured again by archimedes' method. Finally, the gas production (cc/g=cm) was calculated ³ /g) = [ volume after storage (cm) ³ ) Volume before storage (cm) ³ )]Weight (g) of positive electrode active material 100. The gas generation amount is a so-called gas generation amount per unit weight of the positive electrode active material 100, and is therefore an index indicating physical properties (gas generation characteristics) of the positive electrode active material 100, and is a parameter for predicting expansion characteristics of the secondary battery 10.

<4. Theory of derivation of proper range of specific surface area >

Here, a theory of derivation of formula (2) in which an appropriate range of the specific surface area a is defined in relation to the crystallite size Z will be described.

In the case of deriving the formula (2), first, the corresponding relationship between the crystallite size Z and the specific surface area a and the capacity maintenance rate is obtained by examining the capacity maintenance rate (%) while changing the crystallite size Z and the specific surface area a, respectively, according to the procedure of examining the cycle characteristics described above. In this case, the crystallite size z=40.0 nm to 80.0nm, and the specific surface area a=0.40 m ² /g～1.80m ² /g。

Next, the allowable range of the capacity retention rate was set to 85% or more (lower limit value=85% of the allowable capacity retention rate), and the values of the crystallite size Z and the specific surface area a at the capacity retention rate of 85% were determined, whereby these values were plotted.

Next, multiple regression analysis was performed using the results of plotting the crystallite size Z and the specific surface area a, thereby obtaining a first straight line L (solid line L1) shown in fig. 5. Thus, the capacity retention rate can be predicted from the crystallite size Z and the specific surface area a.

Next, the specific surface area a (m ² And/g), thereby obtaining the correspondence of the washing time to the specific surface area A. In this case, the specific surface area a=0.40 m ² /g～1.80m ² And/g. Next, the values of the washing time and the specific surface area a are plotted, respectively, and then linear approximation is performed using these values, thereby obtaining an approximate straight line. Then, the allowable range of the gas generation amount was set to 6cm ³ Not more than/g (upper limit value of allowable gas generation amount=6cm) ³ /g) determining gas using an approximate straight lineThe volume of the produced body is 6cm ³ Specific surface area A at/g.

Then, the specific surface area A was examined while changing the crystallite size Z, and the gas generation amount was determined to be 6cm for each crystallite size Z by the same procedure ³ Specific surface area A at/g. In this case, the crystallite size z=40.0 nm to 80.0nm.

Next, the gas generation amount was plotted as 6cm ³ The crystallite size Z and the specific surface area A at/g, thereby obtaining a second straight line L (broken line L2) shown in FIG. 5. This makes it possible to predict the upper limit value of the specific surface area a associated with the fluctuation of the cleaning time for each crystallite size Z.

Finally, by superimposing the two straight lines L (solid line L1 and broken line L2) on the graph, as shown in fig. 5, the appropriate range Q defined by the solid line L1 and broken line L2, that is, the range shown in formula (2), is derived. The range Q is a range of the crystallite size Z and a range of the specific surface area a in which the capacity retention rate is 85 or more and the specific surface area a becomes an upper limit value with the fluctuation of the cleaning time among the crystallite sizes Z, and is a range theoretically derived by the above-described multiple regression analysis or the like.

<5 > investigation

As shown in tables 2 and 3, when the positive electrode active material 100 including the central portion 110 (lithium nickel composite oxide) and the covering portion 120 (boron compound) was used, the initial capacity, the capacity maintenance rate, and the gas generation amount varied according to the crystallite size Z, the specific surface area a, and the element concentration ratios R1 to R3, respectively.

Specifically, when five conditions (experimental examples 1-1 to 1-12) including crystallite size z=40.0 nm to 74.5nm, specific surface area a=proper range, element concentration ratio r1=0.08 to 0.80, element concentration ratio r2=0.60 to 1.50, and element concentration ratio r3=0.15 to 0.90 are satisfied at the same time, the amount of gas generation by positive electrode active material 100 can be suppressed, and therefore, the primary capacity can be ensured, and a high capacity retention rate can be obtained while suppressing the amount of gas generation, as compared with the case (experimental examples 1-13 to 1-23) in which these five conditions are not satisfied at the same time.

Thus, it was confirmed that the range of the specific surface area a shown in the formula (2), that is, the range of the specific surface area a (the range Q shown in fig. 6) defined in the relation with the crystallite size Z is an appropriate range contributing to the securing of the capacity maintenance rate and the suppression of the gas generation amount.

In particular, in the case where five conditions are satisfied simultaneously, if the specific surface area A is 0.53m ² /g～1.25m ² And/g, a sufficiently high battery capacity can be obtained while sufficiently suppressing the amount of gas generated, and a high capacity retention rate can be obtained.

Further, when five conditions are satisfied at the same time, the residual rate of lithium carbonate is suppressed to be substantially equal to or less than when the five conditions are not satisfied at the same time, and the residual rate of lithium hydroxide is suppressed to be equal to or less than when the five conditions are not satisfied at the same time.

However, as described with reference to fig. 7, the range (range F1) in which the residual lithium component using XPS can be analyzed is relatively narrow, whereas the range (range F2) in which the residual lithium component using the wards method can be measured is relatively wide. Therefore, even if the residual amount of the residual lithium component such as lithium carbonate measured by the batteries method is low, the amount of gas generated may be increased. This is considered to be because, even if the residual amount of the residual lithium component is reduced by ensuring the water washing time in the water washing step, if the baking temperature is increased in the covering step (second baking step), lithium is eluted from the inside of the positive electrode active material 100 (lithium nickel composite oxide), and thus new lithium carbonate is formed in the vicinity of the outermost surface of the positive electrode active material 100. When the warder method having a wide measurable range (range F2) is used, the amount of lithium carbonate in the vicinity of the outermost surface of the positive electrode active material 100 cannot be measured. In contrast, when XPS having a narrow measurable range (range F1) is used, the amount of the gas generation source (eluted lithium) in the vicinity of the outermost surface of the positive electrode active material 100 can be quantified. Accordingly, when the amount of the gas generation source near the outermost surface of the positive electrode active material 100 is large, it is considered that the amount of gas generation increases in the secondary battery 10.

<6. Other evaluation and investigation >

In addition, other evaluations and examinations were performed as described below.

Experimental examples 2-1 to 2-4

As shown in table 4, except that the particle diameters D10, D50, and D90 (μm) of the volume-based particle size distribution of the positive electrode active material 100 were changed, a secondary battery was produced and the battery characteristics (cycle characteristics) were evaluated by the same procedure. In this case, as shown in table 4, the particle diameters D10, D50, and D90 were changed by changing the mixing ratio (weight ratio) of the small particle diameter particles and the large particle diameter particles. Accordingly, the compressed density (g/cm) ³ ) Changes were also made.

TABLE 4

As shown in table 4, when the conditions (examples 1-1, 2-1, and 2-2) of the particle diameters d10=2.8 μm to 4.0 μm, d50=11.8 μm to 14.4 μm, and d90=22.7 μm to 26.3 μm were satisfied, a higher capacity retention rate was obtained than when these conditions (examples 2-3 and 2-4) were not satisfied.

In particular, when the particle diameters D10, D50 and D90 satisfy the above conditions, the compressed density is 3.40g/cm ³ ～3.60g/cm ³ A high capacity retention rate can be obtained.

Experimental examples 3-1 to 3-8

As shown in table 5, except that the particle diameter (μm) of the peak P1 and the particle diameter (μm) of the peak P2 of the volume-based particle size distribution were changed, a secondary battery was produced and the battery characteristics (cycle characteristics) were evaluated by the same procedure. In this case, as shown in table 5, the small-particle-diameter particles and the large-particle-diameter particles were mixed at a predetermined mixing ratio (weight ratio), to obtain the positive electrode active material 100 having two peaks P (P1, P2). The particle diameters D50 (μm) of the small-particle-diameter particles and the large-particle-diameter particles are shown in Table 5. Accordingly, the compressed density (g/cm) ³ ) Changes were also made.

TABLE 5

As shown in table 5, when the conditions of the peak P1 particle diameter=3.0 μm to 7.0 μm and the peak P2 particle diameter=14.0 μm to 30.0 μm were satisfied (examples 1-1 and 3-1 to 3-4), a higher capacity retention rate was obtained than when these conditions were not satisfied (examples 3-5 to 3-8).

In particular, when the particle diameters of the peaks P1 and P2 satisfy the above conditions, the compressed density is 3.45g/cm ³ ～3.70g/cm ³ A high capacity retention rate can be obtained.

<7. Summary >

As described above, when the positive electrode active material 100 including the center portion 110 (lithium nickel composite oxide) and the cover portion 120 (boron compound) is used, the positive electrode active material 100 can obtain excellent gas generation characteristics if the structure and physical properties of the positive electrode active material 100 satisfy five conditions at the same time. Accordingly, in the secondary battery 10 using the positive electrode active material 100, the primary capacity characteristics, the cycle characteristics, and the expansion characteristics (gas generation characteristics) are all good, and excellent battery characteristics are obtained.

The present technology has been described above with reference to one embodiment and example, but the present technology is not limited to the one described in the embodiment and example, and thus various modifications are possible.

Specifically, the case where the secondary battery of the present invention is a laminate film type secondary battery is described, but the type of the secondary battery of the present invention is not particularly limited. Specifically, the secondary battery of the present invention may be, for example, a cylindrical, square, coin-type, or other type of secondary battery.

The effects described in the present specification are principally examples, and therefore the effects of the present technology are not limited to the effects described in the present specification. Thus, other effects can be obtained by the present technology.

Claims

1. A positive electrode active material for a secondary battery is provided with:

a central portion containing a layered rock salt type lithium nickel composite oxide represented by the following formula (1); and

a covering portion covering a surface of the center portion and containing a boron compound,

the crystallite size of the (104) crystal face calculated by using an X-ray diffraction method and Scherrer's formula is 40.0nm or more and 74.5nm or less,

the specific surface area measured by the BET specific surface area measurement method satisfies the condition represented by the following formula (2),

Calculated from a C1s spectrum and an O1s spectrum measured using an X-ray photoelectron spectroscopy and represented by the following formula (3) at a first element concentration ratio of 0.08 or more and 0.80 or less,

based on the Li1s spectrum and Ni2p spectrum measured by the X-ray photoelectron spectroscopy _3/2 Spectrogram, co2p _3/2 Spectrogram, mn2p _1/2 The second element concentration ratio calculated from the spectrum and Al2s spectrum and represented by the following formula (4) is 0.60 or more and 1.50 or less,

from the B1s spectrum, ni2p _3/2 Spectrogram, co2p _3/2 Spectrogram, mn2p _1/2 The third element concentration ratio calculated from the spectrum and Al2s spectrum and represented by the following formula (5) is 0.15 or more and 0.90 or less,

Li _a Ni _1-b M _b O _c ···(1)

m is at least one of cobalt Co, iron Fe, manganese Mn, copper Cu, zinc Zn, aluminum Al, chromium Cr, vanadium V, titanium Ti, magnesium Mg and zirconium Zr, a, b and c satisfy 0.8 < a < 1.2, 0.4 and 0 < c < 3,

-0.0160×Z+1.72≤A≤-0.0324×Z+2.94···(2)

z is the crystallite size of the (104) crystal face, the unit is nm, A is the specific surface area, and the unit is m ² /g，

R1＝I1/I2···(3)

R1 is the concentration ratio of the first element, I1 is CO calculated according to a C1s spectrogram ₃ Concentration, I2 is according toThe O1s spectrum is calculated as Me-O concentration, wherein Me-O is an oxide derived from O bonded to Li, ni or M in the formula (1) and detected in a range of bond energy of 528eV to 531eV,

R2＝I3/I4···(4)

R2 is the second element concentration ratio, I3 is the Li concentration calculated according to the Li1s spectrum, and I4 is the Li concentration calculated according to Ni2p _3/2 Spectrogram, co2p _3/2 Spectrogram, mn2p _1/2 The sum of Ni concentration, co concentration, mn concentration and Al concentration calculated by the spectrogram and the Al2s spectrogram,

R3＝I5/I4···(5)

r3 is the concentration ratio of the third element, and I4 is Ni2p _3/2 Spectrogram, co2p _3/2 Spectrogram, mn2p _1/2 The sum of Ni concentration, co concentration, mn concentration and Al concentration calculated by the spectrogram and the Al2s spectrogram, I5 is B concentration calculated according to the B1s spectrogram,

the concentration is in atomic%.

2. The positive electrode active material for a secondary battery according to claim 1, wherein,

the specific surface area is 0.53m ² Above/g and 1.25m ² And/g or less.

3. The positive electrode active material for a secondary battery according to claim 1 or 2, wherein,

the particle diameter D50 of the volume-based particle size distribution is 11.8 μm or more and 14.4 μm or less.

4. The positive electrode active material for a secondary battery according to claim 3, wherein,

the particle diameter D10 of the volume-based particle size distribution is 2.8 μm or more and 4.0 μm or less, and,

the particle diameter D90 of the volume-based particle size distribution is 22.7 μm or more and 26.3 μm or less.

5. The positive electrode active material for a secondary battery according to claim 3 or 4, wherein,

The compression density is 3.40 g-cm ³ Above and 3.60g/cm ³ The following is given.

6. The positive electrode active material for a secondary battery according to any one of claim 1 to 5, wherein,

the volume-based particle size distribution has two or more peaks.

7. The positive electrode active material for a secondary battery according to claim 6, wherein,

the volume-based particle size distribution has a first peak in a range of a particle diameter of 3 μm or more and 7 μm or less, and has a second peak in a range of the particle diameter of 14 μm or more and 30 μm or less.

8. The positive electrode active material for a secondary battery according to claim 6 or 7, wherein,

compression density of 3.45g/cm ³ Above and 3.70g/cm ³ The following is given.

9. A secondary battery is provided with:

a positive electrode including a positive electrode active material, a negative electrode, and an electrolyte,

the positive electrode active material is provided with:

the crystallite size of the (104) crystal face of the positive electrode active material calculated by using an X-ray diffraction method and Scherrer's formula is 40.0nm or more and 74.5nm or less,

The specific surface area of the positive electrode active material measured by the BET specific surface area measurement method satisfies the condition represented by the following formula (2),

calculated from a C1s spectrum and an O1s spectrum of the positive electrode active material measured using an X-ray photoelectron spectroscopy and represented by the following formula (3) at a first element concentration ratio of 0.08 or more and 0.80 or less,

based on the Li1s spectrum and Ni2p spectrum of the positive electrode active material measured by the X-ray photoelectron spectroscopy _3/2 Spectrogram, co2p _3/2 Spectrogram, mn2p _1/2 The second element concentration ratio calculated from the spectrum and Al2s spectrum and represented by the following formula (4) is 0.60 or more and 1.50 or less,

based on the B1s spectrum of the positive electrode active material measured by the X-ray photoelectron spectroscopy, ni2p _3/2 Spectrogram, co2p _3/2 Spectrogram, mn2p _1/2 The third element concentration ratio calculated from the spectrum and Al2s spectrum and represented by the following formula (5) is 0.15 or more and 0.90 or less,

Li _a Ni _1-b M _b O _c ···(1)

-0.0160×Z+1.72≤A≤-0.0324×Z+2.94···(2)

z is the crystallite size of the (104) crystal face of the positive electrode active material, the unit is nm, A is the specific surface area of the positive electrode active material, and the unit is m ² /g，

R1＝I1/I2···(3)

R1 is the concentration ratio of the first element, I1 is CO calculated according to a C1s spectrogram ₃ The concentration, I2, is a Me-O concentration calculated from an O1s spectrum, wherein Me-O is an oxide derived from O bonded to Li, ni or M in the formula (1) and detected in a range of bond energy of 528eV to 531eV,

R2＝I3/I4···(4)

R3＝I5/I4···(5)

r3 is the concentration ratio of the third element, and I4 is Ni2p _3/2 Spectrogram, co2p _3/2 Spectrogram, mn2p _1/2 Spectrogram and Al2s spectrogram calculationThe sum of Ni concentration, co concentration, mn concentration and Al concentration is calculated according to the B1s spectrogram, I5 is B concentration,

the concentration is in atomic%.

10. The secondary battery according to claim 9, wherein,

the battery further comprises a film-shaped outer packaging member that accommodates the positive electrode, the negative electrode, and the electrolyte.